Caption: Anisakiasis life cycle. Diagram showing the life cycle of the parasitic nematodes (roundworms) that are the cause of anisakiasis. The parasite is common in marine fish. The larvae may move through numerous crustacean, fish and squid hosts before reaching a marine mammal where they mature and produce eggs. Humans can become infected by the parasite by eating raw or undercooked fish. The worms cannot survive in humans. Anisakiasis causes abdominal pain, nausea and vomiting.